Process of dealkylating alkoxy aromatic amines



Patented F eb. 14, 1950 PROCESS OF DEALKYLATING ALKOXYH AROMATIC AMINESCurt G. Vogt, Union, N. J and Franz Marschall, Easton, Pa., assignors toGeneral Aniline -& Film Corporation, New York, N. Y., a corporation ofDelaware No Drawing. Application November 1, 1946, Serial No. 707,328

' 7 Claims. 1 This invention relates to a process of dealkylating alkoxyaromatic amines by the action of an aluminum halide at elevatedtemperatures.

This application is a continuation-in-part of our copending applicationSerial No. 576,708, filed February 7, 1945, now abandoned.

It is known to dealkylate alkoxy aromatic compounds by treatment thereofwith aluminum chloride at elevated temperatures, Houben, Die Methodender Organischen Chemie, 3rd edition (1930) 3, '176. It is also known to'dealkylate alkoxy aromatic amines by subjecting the alkoXy compound asthe free amine to the action of aluminum chloride at. elevatedtemperatures, British Patent 479,865. The reaction is useful for thepreparation of hydroxylated aromatic compounds, the dealkylatedproduct-aluminum chloride complex formed in the reaction being subjectedto hydrolysis for this purpose. The present invention has for an objectim- .reaction is subjected to the action of the aluminum halide'atelevated-temperatures. Suitable mineral acids for the formation of theamine salt are the halogen acids, 1. e., hydrochlori c, hydrobromic,hydriodic and hydrofluoric acid,

sulfuric acid and phosphoric acid. Preferably,

the hydrochloride salt of the alkoxy aromatic airline is employed.Following the process as thus modified, a greater yield of thedealkylated aromatic amine can be obtained than when operating accordingto the prior art process wherein the alkoxy aromatic amine is introducedinto the reaction mixture in the form of the free amine.

The dealkylating reaction in accordance with the present invention canbe carried out by providing a reaction mass which is fluid at reactiontemperatures for which, preferably, an inert liquid organic diluent isemployed. The aluminum halide, which suitably is aluminum chloride or.aluminum bromide, is preferably present in the reaction mixture inexcess of the alkoxy aromatic amine. The temperature at which thedealkylation is effected may vary and suitably may be from about 70 C.to about 220 C- empl ing a liquid organic diluent, the upper limit oftemperature being dependent upon the boiling point of the organicdiluent. In many instances, using a liquid organic diluent, the reactioncan be conveniently carried out by operating at the reflux temperatureof the reaction mixture. Suitable inert liquid organic diluents, are,for example, benzene, nitrobenzene, toluene, nitrotoluene, xylene andthe like.

If it is desired to carry out the reaction at temperatures above about160 C. it is preferable to employ a double salt of the aluminum halideas the combined reactant and diluent. Operating in this way, it ispossible to carry out the reaction at temperatures which range upwardlyt the boiling point or decomposition temperature of the reactants, forexample, as high as 300 C. or higher. Examples of double salts ofaluminum halides which may be employed are those formed from aluminumchloride or aluminum bromide with respectively, amonium chloride,lithium chloride, sodium chloride, potassium chloride, sodium bromide,potassium bromide, cuprous chloride, silver chloride, barium chloride,magnesium chloride, stannous chloride, antimony trichloride, manganouschloride and the like.

The process of the invention may be applied to advantage in dealkylatingmonoor polynuclear alkoxy aromatic amines containing one or more alkoxyand amino groups and which, otherwise, are unsubstituted or contain onlysuch substituents as do not adversely affect the dealkylation, such asalkyl groups. Preferred of such alkoxy aromatic amines are those of thebenzene and diphenyl series, more particularly dianisidine from which bysubsequent hydrolysis of the dealkylateddianisidine-aluminum halidecomplex can be obtained thevaluable dye intermediate;dihydroxybenzidine. Among other alkoxy aromatic amines of the foregoingkind may be specifically mentioned, for example, ortho, meta andpara-anisidine, 4-chloro-o-anisidine, 4-nitro-o-anisidine,3-amino-4-methoxytoluene, 3,-6-dimethoxyaniline, 2 ethoxy 1na'ohthylamine, i-amino-3-methoxy carbazole and the like.

organic diluent has been used in the dealkylating reaction this may beremoved from the aqueous solution of the hydrolyzed product bysteam-distillation and the hydroxylated aromatic amine precipitated fromthe :aqueous solution in the form of asalt such as the sulfate orhydrochloride.

The alkyl groups split off in the dealkylating reaction on cleavage ofthe ,alkoxy group or groups form alkyl halides with the anion of thealuminum halide employed. The alkyl halides of low boiling point such as:methyl chloride or bromide and ethyl chloride or bromide volatilize offfrom the reaction and are of high purity.

The invention is further illustrated by the following specific examplesto which, however, it is not to be limited. Parts are by weight. It isto be understood that in conducting the process, anhydrous or .nearlyanhydrous conditions should be maintained in accordance with soundpractice.

Example .1

50 parts of dianisidine dihydrochloride are charged into 330 parts oftoluene contained in a suitable reaction vessel equipped with a stirrerand a reflux condenser. 21-0 parts of aluminum chloride are added undergood agitation. The mixture is heated to refluxing temperature for aboutone-quarter hour, and then cooled to about 80 :C. parts of dianisidinedihydrochloride are added and the mixture heated to a slight refluxing.After about one-quarter hour, the mass is again cooled to about 80 C.and a further 25 parts of dianisidine dihydrochloride added. The mixtureis again heated to refluxing where it is held for about two hours, afterwhich time the reaction is complete. The lowering of the temperaturebefore each addition of dianisidine dihydrochloride is preferred toprevent violent reaction. During the reaction methyl chloride is formedand escapes from the reaction mass. The reaction mass is cooled andpoured into water, which results in hydrolyz'ing the dealkylateddianisidine-aluminum chloride complex. With the addition of hydrochloricacid to keep the aluminum salts in solution, the aqueous mass from thehydrolysis is subjected to steam-distillation to remove the toluene. Tothe resulting aqueous solution, which is substantially free fromtoluene,

sodium sulfate is added to precipitate the dihydroxybenzidine, which inthe form of its sulfate is separated by filtration. The yield ofdihydroxybenzidine is about 94% of theory. Starting with dianisidine,the yield of the product is about 7 Example 2 48.8 parts o-anisidinehydrochloride is charged in quarter portions into a well stirred mixtureofis about 98% of theory.

. Egample 3 48.8 parts p-anisidine hydrochloride is charged The aqueousin quarter portions into 330 parts toluene and 102.4 parts anhydrousaluminum chloride and treated and worked up as described in Example 2.The yield of p-aminophenol is about 100% of theory.

Example 4 Example 5 A mixture of 96 parts sodium chloride and 218 partsaluminum chloride is melted together at about 160 C. After raising thetemperature of the "melt to about 195 to 200 C., 65 parts dianisidinedihydroc'hloride is added and the reaction mass maintained at thistemperature with agitation for about two hours and then drowned in about2,000 parts of water. To the aqueous mixture with stirring is addedabout 84 parts concentrated hydrochloric acid, and then about 300 partsof sodium sulphate to precipitate the dihydroxybenzidine in the ,form'of its sulphate. The mass is cooled, filtered and washed with a 10%sodium sulphate solution.

As yarious other embodiments of the invention will occur to thoseskilled in the art, it is not intended that the scope of the patent belimited except as is required by the prior art and the appended claims.

We claim:

1. In a process of dealkylating an .alkoxy aromatic amine by heating theamine in the presence of a inert liquid diluent with a compound selectedfrom the group consisting of aluminum chloride and aluminum bromide atelevated temperatures, the improvement which comprises conducting thereaction by employing in place of the free alkoxy aromatic amine thesalt thereof with a mineral acid selected from the group consisting ofthe halogen acids, sulfuric acid and phosphoric acid said temperaturebeing in the range 70 C. to the boiling point of the diluent or thedecomposition point of the amine, whichever is lower.

2. A process of dealkylating an unsubstituted alkoxy alkylaryl aminewhich comprises heating the amine in the form of the salt of a mineralacid selected from the group consisting of the halogen acids, sulfuricacid and phosphoric acid with aluminum chloride at a, temperature in therange 70 to 220 C. in the presence of an inert liquid diluent.

3. A process of dealkylating an unsubstituted alkoxy armoatic aminewhich comprises heating the amine in the form of the salt of a mineralacid selected from the group consisting of the halogen acids, sulfuricacid and phosphoric acid with aluminum chloride at a temperature in therange 70 to 220 C. in the presence of an inert liquid diluent.

4. A process of dealkylating an unsubstituted alkoxy phenylam'ine whichcomprises heating the amine in the form of the salt of a mineral acidselected from the group consisting of the halogen acids, sulfuric acidand phosphoric acid with aluminum chloride at a temperature in the range70 to 220 C. in the presence of an inert liquid diluent.

5. A process of dealkylating an unsubstituted alkoxy diphenylamine whichcomprises heating the amine in the form of the salt of a mineral acidselected from the group consisting of the halogen acids, sulfuric acidand phosphoric acid with aluminum chloride at a temperature in the range70 to 220 C. in the presence of an inert liquid diluent.

6. A process which comprises heating dianisidine dihydrochloride withaluminum chloride at a temperature in the range 70 to 220 C. in thepresence of an inert liquid diluent.

7. A process of preparing dihydroxybenzidine which comprises completelydealkylating dianisidine heating the dihydrochloride thereof withaluminum chloride in the presence of a inert liquid diluent at anelevated temperature and hydrolyzing the resulting dealkylateddianisidene-aluminum chloride complex said temperature in the range 70C. to the boiling point of the diluent or the decomposition point of theamine, whichever is lower.

CURT G. VOGT. FRANZ MARSCHALL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Kolhatkar et al.: Chem. Ab., 26, page 113 (1932).

Popov: Chem. Ab., 30, page 1049 (1936).

Fieser et al., Organic Chemistry (D. C. Heath and Co., Boston, 1944),page 639.

1. IN A PROCESS OF DEALKYLATING AN ALKOXY AROMATIC AMINE BY HEATING THEAMINE IN THE PRESENCE OF A INERT LIQUID DILUENT WITH A COMPOUND SELECTEDFROM THE GROUP CONSISTING OF ALUMINUM CHLORIDE AND ALUMINUM BROMIDE ATELEVATED TEMPERATURE, THE IMPROVEMENT WHICH COMPRISES CONDUCTING THEREACTION BY EMPLOYING IN PLACE OF THE FREE ALKOXY AROMATIC AMINE THESALT THEREOF WITH A MINERAL ACID SELECTED FROM THE GROUP CONSISTING OFTHE HJALOGEN ACIDS, SULFURIC ACID AND PHOSPHORIC ACID SAID TEMPERATUREBEING IN THE RANGE 70*C. TO THE BOILING POINT OF THE DILUENT OR THEDECOMPOSITION POINT OF THE AMINE, WHICHEVER IS LOWER.